1. Field of the Invention
The present invention relates to a thrust bearing for use in a rolling mill having a pair each of working rolls and stay rolls as well as a mechanism for crossing the rolls.
2. Related Background Art
FIG. 5 shows in cross-section a main portion of a four-stage rolling mill which is a kind of conventional rolling mills. In FIG. 5, an upper working roll 102 and a lower working roll 103 are located vertically adjacent to each other. Above the upper working roll 102, there is arranged an upper stay roll 101, while a lower stay roll 104 is arranged below the lower working roll 103. A material to be rolled is passed between the upper and lower working rolls to be rolled in an appropriate thickness, where bending of the upper and lower working rolls, occurring due to the reaction of the rolling is prevented by the upper and lower stay rolls. It should be noted that the left side of FIG. 5 constitutes a driving side provided with a driving mechanism (not shown) for transmitting a rotating force to the rolls, while the right side of the same is made dismountable for maintenance or the like. Therefore, each of the rolls is rotatably supported by an upper stay roll chock 111, an upper working roll chock 112, a lower working roll chock 113, or a lower stay roll chock 114, respectively. These roll chocks are attached to a mill housing (not shown) which is a rigid body.
In recent years, a new type of rolling mill has been developed for the purpose of improving the plate manufacturing accuracy. Such a new type of rolling mill having a cross mechanism will be briefly explained with reference to FIGS. 3 and 4. FIG. 3 shows a main portion of the rolling mill having a cross mechanism, viewed from one side thereof. FIG. 4 shows a top plan view of a roll which is swung by the cross mechanism.
Conventional rolling mills have a problem that the thickness of a rolled material near the ends of a roll tends to be smaller than that of a central portion of the roll. To solve this problem, rolls have been provided with a crowing, a roll bending mechanism has been equipped between upper and lower roll chocks, and so on. However, the improvement in the plate manufacturing provided by these methods was limited. The new type of rolling mill is constructed such that an upper working roll and an upper stay roll are swung or crossed with respect to a lower working roll and a lower stay roll, and the rolling is performed in this state. Explaining with reference to FIG. 4, a one-dot chain line X--X represents the axis of the upper working roll and the upper stay roll, while a one-dot chain line Y--Y represents the axis of the lower working roll and the lower stay roll (not shown). An angle formed by both the axes is designated .alpha.. By adjusting this angle .alpha., that is, by appropriately swinging the rolls, a material can be rolled in a uniform thickness.
Referring now to FIG. 3, an upper stay roll chock 111 is downwardly urged through a thrust bearing 107 by a pressing device 105 which may be a hydraulic device, by way of example. Likewise, a lower stay roll chock 114 is attached to a mill housing 106 through a thrust bearing 108. A cross mechanism, not shown, causes each of the rolls and each of roll chocks to swing.
Incidentally, moving the pressing device 105 and the mill housing together with the roll chocks and so on causes the apparatus to be undesirably large and complicated, so that a thrust bearing need be inserted between the roll chocks and the pressing device or the mill housing. However, since the relative motion thereof is not linear motion but swing motion, a normal direct-acting rudder bearing cannot be used for this purpose. Moreover, this portion is an important portion which is applied with a large load, so that measures should be taken to prevent defective operation of the bearing.